ISSN:0886-9375    

DOI:10.1002/rrr.3450010102

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe Danish Watercourse Law of 1982 states that major river works and maintenance procedures must be planned and undertaken with regard to water quality and the physical form of the river channel. Fluvial geomorphology is an essential component of alternative procedures of river management which work with nature rather than against it. A survey of Danish stream channels has been produced by collating data obtained from maps, field surveys and engineering documents. This indicates that 97.8 per cent of Danish watercourses have been artificially straightened and that only 2.2 per cent (880 km) have natural morphological characteristics. The density of channel works is 300 times greater than in the U.S.A. and 15 times greater than in England and Wales. It is suggested that since there are only a few naturally sinuous channels in Denmark these should be given special consideration with regard to stream management practices. Measurements undertaken at approximately 300 sites in Denmark indicate five major processes of adjustment within straightened reaches. These adjustments include degradation of the channel bed with associated bank slumping, armouring of the bed, the development of a sinuous thalweg by the deposition of sediment at low gradients, and restoration of meanders. Channel stability is related to specific stream power and the results may be useful in predicting potential adjustments following channel straightening. Deposition in natural reaches below straightened channels often obliterates pool and riffle sequences but several channel adjustments may provide a greater variability of physical habitats than the initial uniform straightened channel; their significance for the biology of the watercourse is best considered before traditional management practices are carried out to control the adjustment.

ISSN:0886-9375    

DOI:10.1002/rrr.3450010103

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe hydrosystem of the Rhǒne River, France, is considered in 3 dimensions: the upstream‐downstream progression, the transversal dimension (main stream, side‐arms, marshes, flood plain and their interconnections), and the vertical dimension (relationships between epigean and ground waters). Emphasis is placed on the temporal dimension, which considers changes in the river's dynamics, and on the development of its ecosystems over several centuries.Analyses were performed on different spatial scales; the definitions of functional sectors, functional sets and functional units are based on a combination of geomorphic patterns, fluvial dynamics and ecological processes. Synchronic and diachronic analyses were carried out using functional describers (granulometry and organic content of sediments, floral and faunal communities).These studies deal mainly with the distrubed hydrosystems of regulated rivers. The changes of the ecological successions are focused on after reference to natural models and the reconstitution of ancient human disturbances. Predictive scenarios are proposed to promote ecological management of the alluvial plains in the event of hydroelectric develop

ISSN:0886-9375    

DOI:10.1002/rrr.3450010104

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe modes of colonization of a heterogenous alluvial area byPhalaris arundinacea L., a pioneer species, were studied on the edge of the Garonne river downstream of Toulouse (S.W. France). The heterogeneity of the location is essentially represented (1) by the type of soil: sands and gravels on the banks of the Garonne and silts in the hollows at a certain distance from the river; (2) by the period of submersion: zones flooded only during short periods and zones submerged during six months of the year; and (3) by the fertility of the substratum.The response of thePhalaris arundinaceapopulation were measured using vegetation structure parameters and descriptions of the development cycle. Water plays the most important part in the identification of space colonization modes. Two types of individual plants appear. Those living in submerged environments for a very short time are characterized by both a high biomass and sexual reproduction energy allowance, and by unimodal growth. Those living in environments flooded over long periods are characterized by both a low biomass and sexual reproduction energy allowance, and by a bimodal growth in two successive generations: a submersion generation and a low‐water generation. Specific competition reduces the differences between the two types of individual plants from the point of view of population cover and of the structure and density of the individual plants.Phalaris arundinacea L. is shown to have a remarkable capacity for colonizing sites with distinctive ecological characteristic

ISSN:0886-9375    

DOI:10.1002/rrr.3450010105

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractAn attempt is made to appraise the present and likely future environmental impacts of the Tucuruí Dam upon the mid and lower Araguaia‐Tocantins Basin (Brazilian Amazonia). Information has been obtained by literature review and from field visits made by the author in 1981, 1983, and 1985. The problems of impoundment‐related environmental impact assessment in tropical developing countries are also discussed.Tucuruí is the world's fourth largest hydroelectric project and is the first large dam to be completed in an Amazonian rainforest environment. It is also the first of a number of large dams which Brazil plans to construct in the Araguaia‐Tocantins Basin and on other tributaries of the Amazon. The appraisal of problems associated with Tucuruí Dam should help planners minimize difficulties with future Amazonian hydroprojects.Like many developing country environmental impact assessments, that carried out at Tucuruí was begun after the construction site had been selected and construction had begun. Tucuruí impact studies have tended to concentrate on the environmental and socioeconomic impacts generated in the vicinity of the dam and reservoir; downstream impacts have received less attention but are already apparent. Major impacts identified include reservoir siltation, disruption of fisheries and agriculture (especially floodland cultivation) downstream, and human diseas

ISSN:0886-9375    

DOI:10.1002/rrr.3450010106

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractRiverine trichopteran (caddisfly) communities were sampled seasonally at eight locations over a two‐year period to determine if a multiple‐level release hydroelectric dam created a faunal discontinuity along the longitudinal profile of the Clearwater River in northern Idaho. The confluence of a non‐regulated river with a regulated reach provided an unusual opportunity to examine the recovery of community parameters in a semi‐regulated river.A marked discontinuity in the caddisfly community occurred in the regulated reach immediately below the dam, reflected by greatly reduced diversity and abundance values, and by shifts in functional relationships. These faunal changes are primarily attributable to the modified temperature, discharge, and food resources induced by river regulation. The non‐regulated river exerted a major mitigative effect on the trichopteran fauna below its confluence with the regulated reach, despite maintenance of semi‐regulated conditions. Trichopteran community parameters approached near normal levels concomitant with partial reductions in flow fluctuations, and partial recovery of temperature and food resources. In addition, the non‐regulated river provided an important colonization pathway for riverine species to enter the semi‐regulate

ISSN:0886-9375    

DOI:10.1002/rrr.3450010107

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe particle‐composition (0.15 to>64 mm) of the stream‐bed was monitored by Surber sampling at sites above and below the site of the Thomson Dam during the two years of most active construction. Levels of particles between 0.5−2 mm were highest 9.5 km below the dam site, and increased throughout the study. Levels of these grades at sites above and well below the dam site were variable, but showed no consistent trends. Material greater than 2 mm showed no substantial variation either over time or between sites spanning approximately 70 km of river length and 250 m of elevation.Artificial substratum samplers were used to estimate the rate of sediment input (0‐2 mm) between sampling dates. Sediment input was clearly highest 1 km and 9.5 km below the dam site. Input was seasonal, with maxima in winter and spring of each year. Size classes 1‐2 mm and<0.063 mm contributed over 60 per cent of the total deposited sediment. Over the second year of the study, high levels of sediment<0.063 mm were deposited at a site 33 km below the dam site, indicating the progressive movement of material down the river.Some fine sediment was found to penetrate unconsolidated bed material to depths down to 60 cm. It is suggested that such material, resulting from land disturbance, is capable of filling interstitial spaces in the stream‐bed, and that major disturbance of the bed may be necessary to

ISSN:0886-9375    

DOI:10.1002/rrr.3450010108

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractData for three rivers in the upper Severn catchment are examined to assess the influence of regulation strategies on the thermal characteristics. Seasonal and diel temperature variations are markedly influence by the release discharge and the depth of withdrawal from the reservoir. The downstream influence of river regulation is confined to a relatively short reach (ca. 30 km) below the dams. Nevertheless, the control of water temperature during hot, dry summers could benefit salmon populations.

ISSN:0886-9375    

DOI:10.1002/rrr.3450010109

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450010110

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450010111

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY